I Solemnly Swear That I Am Up To No Good
by Tia151
Summary: James and Sirius are best friends, but when Prof. McGonagall gives James a detention for something Sirius did, it's time to get revenge. This is my first story and I'd really like to know what you think, so please leave a comment :D - Tia [COMPLETE]
1. Chapter 1 - ChocoBalls

"But, Professor," James whined. "It was Sirius. He was the one teasing the Mandrake."

"I've heard enough James." McGonagall snapped. "You will see me after dinner, my office, and will stay until all those books are re-ordered alphabetically."

There was no arguing; this was McGonagall. James didn't care how much Sirius apologized, he was getting his revenge.

Sirius woke early the next morning, he had not been able to speak to James since the Transfiguration Lesson yesterday. He glanced over to James' bed across the room; it was empty, of course. But, Sirius knew where to find him. Quickly, Sirius dressed and proceeded downstairs. He walked through the Gryffindor Common Room, jogged past the Great Hall, ran across the wooden bridge, and practically sprinted towards the Whomping Willow. Just as Sirius has suspected, James was sitting underneath it, twirling his wand around in his fingers. "I was starting to think you wouldn't come," James said, looking expressionless into the gushing water. "Would've been such a waste of money. Chocoball?" He picked a small, brown paper bag out of his pocket and offered it to Sirius. Cautiously, Sirius plucked a large, round one from the top and popped it - whole - into his mouth. Suddenly, Sirius started spluttering and coughing, his face turning red. "What did you put in them?" Sirius spluttered, as his face turned the colour of a ripe tomato. James looked at Sirius for a moment, smiled and said "Oh, you know, Chocolate, Honeycomb and a hint of Bloodroot."

"Bloodroot!" Sirius repeated stunned, his head now a lovely shade of plum.

Sirius and James both decided then and there that they were now engaged in the fiercest of wizarding prank wars!


	2. Chapter 2 - Sleeping Powder

Sirius was determined to get James back for what he did. Yesterday, after a brief trip to the hospital wing, he had concocted a marvellous scheme that included a pillowcase, a torch and sleeping powder. He was certain this prank would make James rue the day he crossed Sirius Black.

At 6:30pm, Sirius crept into the boys dormitory. Carefully, he removed James' red and gold pillowcase and poured a light sprinkling of sleeping powder over the pillow. He replaced the case, quickly, and slithered out again.

That evening was so tense, that if you so much as breathed, the room would explode. However, Sirius was smiling to himself as he climbed into bed, for whilst everyone was enjoying a bit of silence, James would be sleeping like a log.  
Everyone was up early the next morning for, although it was dark and gloomy weather, there was a Gryffindor Quidditch match later on. Well, everyone but James, who was snoring contentedly in the corner. Sirius looked at James as he was exiting the room and chuckled at James' obliviousness. Sirius then went on to the match, which Gryffindor lost due the absence of their Seeker.  
When James woke up, two days later, he was extremely angry and composed a plan...


	3. Chapter 3 - Crazy Gerbils

A week after the Sleeping Powder incident, objects started to go missing. The first of which was a bungee cord; then a bucket; and finally a cage of Gerbils that the first years were trying to transfigure into mice. Nobody knew where they were going, or who took them, but everyone wanted to find out…

Sirius was expecting a prank from James however, it had been ages since the last one, so Sirius wasn't being a careful as he probably should have been. By now, the news of the disappearances were all over the school; it had spread like wildfire! Sirius would normally traced this back to James straight away but, he wasn't thinking clearly at the moment as his mind had been twisted and warped with paranoia. Sirius spent most of his time sitting with his back to the wall in the corner of the common room and only left when absolutely necessary.

Meanwhile, in the room of requirement, James stood looking at a bungee cord, a bucket and a cage of crazy Gerbils. "Tonight, Sirius will regret pranking me..." he said smugly to himself.

At 7:00pm on the dot, the dinner bell rang and Sirius, slowly, crept out of his battered, red chair. As soon as Sirius had left, James crept into the room carrying the missing objects and, carefully, placed them so the Gerbils were hanging over the chair, poised to fall. He then tiptoed out again.

When Sirius came back, for some unknown reason, he did not notice the Gerbils hanging over his chair, nor the large bungee cord next to it. So, when he sat down the cage swung down gracefully and he came face to face with one of the gerbils. Sirius screamed so loud that night that you'd be able to hear him clearly in Hogsmeade! To make matters worse, at that moment, the entirety of Gryffindor charged into the common room."Ooooooh! Gerbils!" A small boy called Peter Pettigrew cried,"Personally, I've always preferred Rats, but still."

Now, the whole school new about the prank war, and it was starting to get serious...


	4. Chapter 4 - School Ties

James had always been rather sensitive, and had many allergies such as: ponies, horses, dust, nuts, egg and fish. His nose, you could say, was not his strong point. Only his closest friends knew this so, Sirius thought he would use it to his advantage.

It was Sunday, and James had a quidditch practice before lunch. At 10 o'clock, James went out in his quidditch uniform and left his school clothes on his bed. Quickly, Sirius entered and went over to James' bed. He took a pepper shaker out of his pocket and slowly started to grind over the tie. After a few moments, Sirius crept back out of the room and hid the pepper shaker.

When the next day came, the boys dressed and went downstairs for breakfast. They were all eating rather happily when suddenly, James began sneezing uncontrollably! Sirius was laughing his head of and started turning blue in the face. Professor McGonagall rushed over to them but instead of helping James, she turned and shouted at Sirius! "I suppose you think this is funny, don't you, Sirius? I suppose you think this is a joke? Well, he could be dead!" And with that she turned to James. "Detention for a month, Mr Black!"

"Now we're even," thought Sirius as he skulked off. But, James was thinking something different entirely...


	5. Chapter 5 - Talking Shoes

The next day dawned clear and bright; not a cloud in the sky. James was snoozing in the library after a late night reading session. He had been looking into charms and hexes that he could play on Sirius. After three hours of searching through endless books, James had found absolutely nothing suitable. Apprehensively, he turned the page and saw it! A Talking Spell! This charm would enable any object to speak freely and he decided it would be perfect for Sirius' shoes! He spent the day rehearsing the spell on various objects until he was kicked out of the library due to a particularly talkative coat-hanger called 'Hank' who claimed to be 'The High Emperor of the World'. But by then though, James was ready.

He slowly crept up the stairs, ignoring the Hanks insults of 'Filthy peasant! Don't you know your leader?' When James reached the boys dormitory, he found Sirius' shoes and cast the spell: "Disputatio!" He then slipped, silently, into his bed.

On the following morning, Sirius put his shoes on like normal, but was shocked to hear them say "Ouch!" every time he made a step. It took all his patience to stagger to the Great Hall without throwing them out of the window! However, when he arrived, he got no sympathy from his classmates who were laughing their heads off at the sarcastic comments coming from under the table.

As he grew more impatient, a devilish plot was hatched in his mind…

 **Hello! Thank You for reading this chapter! Please let me know what you think – I love to hear from you!**

 **Tia**


	6. Chapter 6 - The End

Chapter Six: The End

 **Disclaimer: None of the characters, places or anything else belonging to the original Wizarding World are mine! (Even if I wish they were)**

 **Hi... I'm Tia and I just wanted to say a quick thank you to all of you! It's been almost 2 years (aaaaaaah) since I first started this story and it's safe to say that the support I've gotten has been nothing short of phenomenal (despite my terribly inconsistent writing habits). So, I feel it only fair that I bring this story to a conclusion. I hope you enjoy it!**

 **Tia :D**

James and Sirius, the idiots that they were, had been embraced in this so-called "Prank War" for far too long and the whole school was facing the consequences. So, after much deliberation, Lily Evans decided that she needed to put a stop to it once and for all, but how?

Needing inspiration, the redhead subconsciously made her way towards the library; a natural instinct after the amount of time she'd spent there over the years. Stuck deep in thought, she found herself approaching the Charms section – one of her favourite places to study. Only now realising what she was doing, Lily took a book named "An Incomplete History of Uncommon Charms and Spells" from one of the towering, dusty shelves. Flicking through it Lily spotted two rather appealing appealing entries and set about spending the remainder of the day researching them.

It was only when the birds had stopped singing and the sky was dark that Lily realized how long she'd been in the library. Luckily, Madam Finchwood had left promptly at 8 o'clock (the official closing time), so Lily wouldn't get caught by her, however there was still the threat of Filch. She would need to be careful. Picking up her notes, Lily crept to the wooden door. "Alohamora." she whispered and the door creaked open, letting her slip out.

When dawn broke, Lily was ready. She dressed and brushed her teeth. " _Today, those morons will finally get their just desserts,_ " she told herself. Wand in hand, she strode down the corridors until she reached the Great Hall. There was no sign of the said " _Morons_ " yet, but that was to be expected – they were teenage boys, after all. Quietly sitting down at the Gryffindor table, Lily found herself incapable of eating her breakfast due to nerves. Fortunately, Lily had decided upon performing the spell silently and therefore anonymously – she didn't need a detention from McGonagall, or any more attention from Potter for that matter.

After waiting 20 minutes, Lily was about to give up and began to stand. When she noticed a certain jet-black haired boy sitting down approximately 12 people down the table. _Potter._ As if, hearing his cue Black entered, ignoring the angry looks he was getting from his past friend, and slid into a seat, 5 people to Lily's other side. Retaking her own place, Lily prepared to set her plan in action. Casting a final glance in each of the boy's directions, she fastened her eyes decidedly shut and cast the first spell. _"Anteoculatia_ " she cursed in her mind. Laughs began to ring out around the hall and Lily opened one eye. To her delight, Potter had suddenly sprouted a magnificent pair of antlers and judging by the cacophony coming from her other side it would appear Black had too. Smiling to herself, Lily once more closed her eyes. " _Cantis_ " came the second spell, once more in her mind. Through the laughs cut two loud voices; "Hogwarts, Hogwarts, Hoggy Warty Hogwarts," they began. Lily couldn't hold in her laughter any more. A combination of a chuckle, giggle and howl erupted from her and all those watching. " _Finally someone got them back for all their ridiculous pranks._ " She thought.

Later that evening, Lily was walking back to her dormitory with Mary Macdonald (one of her closest friends) who was animatedly reenacting her reaction to breakfast's drama. As soon as they entered the warm common room however, Lily stopped in her tracks. Sitting by the blazing fire was Remus Lupin (the only sensible marauder in her opinion), looking directly at her wit ha perplexed look on his face. "Hello Lily, Mary." He said, smiling. "Can I steal Lily from you for a moment, Mary?" The black-haired girl looked questioningly at her friend before nodding and leaving up the stairs. Remus waited until the door of the dormitories had closed behind the girl, then turned to face the guilty-looking Lily. "Funny things aren't they?" He asked, "Non-verbal spells. I mean only a handful of people at this school can use them." Lily raised an eyebrow.

"I'm sure I don't know what you mean." She replied, panicking inside.

"Hmmm," he said, obviously thinking. "Good thing whoever performed the spells this morning was careful. I can only imagine what could have happened had they got it wrong. Anteoculatia and Cantis was it?"

"Yes," she confirmed before realising what she's said, clamping a hand over her mouth and turning bright red "Please don't tell Mcgonagall."

"Don't worry, I simply wanted to thank whoever did it – James and Sirius have finally made up and called off the prank war!" Remus laughed. Lily let out a breath of air that she hadn't realised she'd been holding.

"Thank God," she sighed. Waving goodbye to Remus, Lily made her way up to bed. She's sleep well tonight knowing that _finally_ someone had beaten Potter and Black at their own game. Little did she know that her dealings with the two boys were far from over.

 _ **Fin.**_ **Thanks again for sticking with me through this rather strange (and at times badly-written) story. I hope I managed to bring some kind of joy to you whilst reading it.**

 **See you through the internet,**

 **Tia :D**


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